1. Field of the Invention
The invention relates to methods and apparatus for the catalytic conversion of the exhaust discharge from internal combustion engines, particularly gasoline-burning engines.
2. The Prior Art
The automobile has been identified as one of the principal causes of air pollution. It has been recognized that in order to minimize this pollution catalytic conversion of harmful hydrocarbons, carbon monoxide and nitrogen-oxygen emissions to nitrogen, carbon dioxide and water is desirable. In fact, beginning with the introduction of the 1975 model year automobiles, catalytic converters have become standard equipment.
The catalytic converters now in use for automobiles in this country are based upon the use of the precious metals platinum and palladium as catalysts. These metals are rare and expensive. The United States produces substantially less of these metals than it consumes and is therefore dependent upon foreign sources for these key exhaust catalysts necessary for the control of air pollution caused by the exhaust discharge of internal combustion engines.
The presently used platinum and palladium catalysts have the additional disadvantage of being sensitive to lead which is a common gasoline additive. As a result, the United States government has mandated that new automobiles use only non-leaded gasolines and that a very expensive program of providing separate leaded and non-leaded gasoline be undertaken. A catalyst with substantially less sensitivity to lead poisoning is desired.
There are other applications, such as in underground mining and tunnelling where it is desirable to use internal combustion engines but where hydrocarbons and carbon monoxide products of combustion cannot be tolerated. A suitable, low cost catalyst for the oxidation of hydrocarbons and carbon monoxide is needed for these applications.
While it has been known for some time that copper has a strong catalytic effect in oxidation reactions, copper has not been commercially accepted as a catalyst for catalytic converters because the cost of equipment providing a suitable support for the copper catalyst to give adequate contact with the exhaust discharge and impregnating the copper onto the support is such that the cost advantage between use of a copper catalyst and a precious metal catalyst is not enough to warrant the use of copper over precious metal. That is, while copper is a suitable catalyst metal, its disadvantage in comparison to platinum or platinum-palladium is sufficiently large, considering the overall cost of the catalyst, including support preparation, that it has not attained commercial acceptance.
It is well known that copper as an oxidation catalyst is often modified by the addition of other metals. Specifically, copper chromite has been extensively tested in automotive catalytic converter applications and found to be more effective than copper alone.
In the catalytic conversion of exhaust from internal combustion engines, in addition to the oxidation of hydrocarbons and carbon monoxide, it is desirable at the same time to reduce nitrogen oxides. A separate catalyst, particularly a nickel containing catalyst, in combination with the oxidation catalyst, has been suggested for accomplishing this. It would clearly be very desirable to accomplish both catalytic activities on a single support. By this means, a substantial savings in catalyst cost can be effected.
Accordingly, it is a principal object of this invention to provide a catalytic material for catalytic conversion of the exhaust discharge of an internal combustion engine for which a separate support to provide adequate catalyst surface contact area is not required, which is otherwise more economical than conventional catalysts, which may be modified to function as both an oxidation and reduction catalyst, and which is less sensitive to lead poisoning than conventional catalysts for this purpose.
It is a further objective of this invention to provide a catalytic converter incorporating the catalytic material of this invention.